1. Field of Use
This invention relates generally to a high-pressure hydraulic system and to a self-cleaning filter assembly therefor. In particular, it relates to a high-pressure hydraulic system such as is used, for example, in a large machine, such as a mining shovel or construction machinery or the like, to effect and control movement of large, heavy components in the machine.
2. Description of the Prior Art
Some large machines, such as mining shovels or construction or the like, employ various large, heavy, movable components which are movable or swingable in opposite directions by means of large hydraulic motors, such as extendible/retractable, double-acting, large hydraulic cylinders or rams. Such components may comprise, as in the case of a mining shovel for example, a boom, a stock and a shovel or scoop. Frequently, because of the size and weight of a single component, a pair of hydraulic cylinders mechanically and hydraulically connected in parallel with each other are employed to move that component. The hydraulic cylinders are operated and controlled by a high-pressure hydraulic control system in which they are incorporated and such a system typically comprises a hydraulic fluid reservoir, one or more high-pressure pumps (driven, for example, by the prime mover on the machine), various control valves and pressure relief valves, and filters to remove contaminants from the hydraulic fluid circulating through the system. Contaminants take the form of very small particles of metal and other materials, such as neoprene and teflon, from which the hydraulic cylinders are constructed and which wear away during operation of these components. Even though high-pressure hydraulic systems usually employ filters to filter out such contaminants, the prior art arrangement and location of such filters still enables some of these contaminants to be circulated through the hydraulic system from one system component to another wherein they can cause damage to or malfunction of that system component. In some cases, as where a pair of hydraulic cylinders are connected in parallel, catastrophic mechanical failure of one cylinder resulting from contaminants can sometimes result in failure of the parallel cylinder with resultant risks of human injury and other system damage, as well as expensive repairs. In some prior art high-pressure hydraulic systems, for example, a final filter is installed immediately upstream of a fluid system component to be protected, and this filter is downstream of the system's main filter which is usually near the fluid reservoir. Nevertheless, debris exchange may still take place upstream of the final filter. A further problem with some commercially available filters used in high-pressure systems is the tendency of the filter, either because it is clogged or because of its special configuration, to collapse when subjected to high-pressure fluid flow therethrough, thereby resulting in a non-effective filter or, in some cases, interference with proper fluid flow through the system. Therefore, in some cases an internal by-pass valve is provided which permits flow to reach critical components even if the filter becomes clogged with contaminants.